This invention relates to the field of agriculture and biological control of insect pests. In particular, the invention provides an apparatus and method for low-cost mass production of insecticidal nematodes.
Heightened awareness of the dangers of chemical insecticides, combined with passage of the Federal Food Quality Protection Act restricting usage of these insecticides, has further increased the need for alternative insect control measures. Use of biological insecticides, in particular entomopathogenic nematodes, are consequently becoming an increasingly viable alternative to control insect pest populations.
Nematodes are simple, colorless, unsegmented roundworms that lack appendages. They may be free-living, predaceous or parasitic. The entomopathogenic nematodes of the genera Steinernema and Heterorhabdititis are insect parasitic nematodes that possess an optimal balance of attributes to enable their use as biological control agents for insect pests.
Steinernema and Heterorhabditis have similar life cycles. The non-feeding infective juvenile seeks out insect hosts and penetrate into the insect body. There the juvenile releases a symbiotic bacterium, (i.e., Xeneorhabdus for steinernematids, Photorhadbdus for heterorhabditids), which multiplies rapidly and causes insect death. The nematodes feed upon the bacteria and liquefying insect, and mature into adults. The life cycle is completed in a few days, and hundreds of thousands of new infective juveniles emerge from the insect cadaver in search of fresh insect hosts.
Numerous benefits are derived by the use of nematodes as opposed to chemical insecticides or other biological methods. For example, nematodes are lethal to a greater number of important soil insect pests but are completely safe for plants and animals. Further, most chemical insecticides and biologicals require days or even weeks to kill insect pests, whereas nematodes usually kill most insect pests within 24-48 hours.
The two genera of entomopathogenic nematodes comprise nearly 30 species that are useful as biological control agents against a large number of insect pests, including artichoke plume moth, root weevils, cranberry girdler, sciarids, wood borers, fungus gnats, scarabs, mole crickets, billbugs, army worms, cut worms and web worms.
Unfortunately, for nematodes to represent a commercially viable alternative to chemical insecticides a self-contained, low cost system of production is preferable, if not necessary. Current methods of nematode production require tedious multi-step procedures involving sterilization techniques and expensive equipment, resulting in high production costs and contamination problems.
Moreover, although some of the above-described systems have been used on a small scale, a major difficulty arises when scale-up of nematode production is attempted. In vivo systems have proven difficult to scale-up. In the laboratory, the White trap has been the traditional method of collecting entomopathogenic nematodes. In the White trap, infected insect cadavers are placed within a topless petri plate and the plate is placed in a tray of water. As the nematodes complete their development and emerge to seek new insect hosts, they exit the cadaver into the tray of water and are unable to escape. Nematodes are thus collected in the tray water. Scale-up of harvesting has consisted of simply providing larger White traps, usually by placing several dishes within a large tray. Emerging infective juveniles pass through the disk and settle at the funnel bottom where they are collected by opening the stopcock.
In the natural lifecycle of entomopathogenic nematodes, juveniles infect and kill host insects, multiply and grow to adulthood inside insect cadavers, then produce new infective juveniles that burst from the cadavers and exit into the surrounding medium. In the absence of expensive centrifuges, infective juveniles have traditionally been allowed to settle by gravity, the supernatant is then poured off and either replaced by freshwater or the nematodes are concentrated into a paste for formulation. The settling process in a large volume is time consuming, resulting in anoxic conditions which stress the nematodes.
Therefore, the need exists for improved apparatus and methods for in vivo separation of insecticidal nematodes from bacteria, insect cadavers and debris associated with growth medium used in the harvesting of infective juvenile nematodes.
An object of the present invention is to provide an apparatus for the separation of nematodes from a suspension comprising a reservoir tank for holding nematode suspension; a distribution manifold for dividing the flow of the nematode suspension into individual streams; a control valve for regulating flow; a screen; and a nematode slurry collector (hereinafter referred to as collector).
Another object of the present invention is to provide a method for the production of a nematode slurry comprising introducing a nematode suspension into an apparatus comprising a reservoir tank for holding nematode suspension; a distribution manifold for dividing the flow of the nematode suspension into individual streams; a control valve for regulating flow; a screen; and a collector for collecting nematode slurry, wherein the nematode suspension is present in a holding tank. Then, pumping the nematode suspension from the holding tank into the reservoir tank; feeding the nematode suspension into a distribution manifold; flowing nematode suspension out small openings on the distribution manifold onto a screen; passing the nematode suspension through the screen into a collector, wherein the nematodes are deflected by the screen but do not pass through the screen, and wherein the waste water passes through the screen; discarding waste water containing bacteria and debris through an outlet pipe; collecting nematodes on the screen to produce a nematode slurry; and collecting the nematode slurry in a collector.